Add `__noreturn__' and `__unused__' attributes where appropriate to
the games.
This merges in all such remaining changes from the Linux port of the
NetBSD games, except in hunt (where substantial changes from OpenBSD
need to be looked at).
Most noreturn attributes were previously added in bin/6144, with some
others that were missed then in bin/8082. Previous `unused'
attributes were covered in bin/6557, bin/8058 and other PRs (all these
PRs have already been handled and closed).

Add use of `const' where appropriate to the games.
This merges in all such remaining changes from the Linux port of the
NetBSD games, except in hunt (where substantial changes from OpenBSD
need to be looked at).
Some such changes were previously covered in PRs bin/6041, bin/6146,
bin/6148, bin/6150, bin/6151, bin/6580, bin/6660, bin/7993, bin/7994,
bin/8039, bin/8057 and bin/8093.